lyon] the hares and their allies 339 



notch. Lcpiis yarkandensis from central Asia has postorbital 

 processes agreeing with those of PoBcilolagus. 



2. The skulls having postorbital processes most nearly resembling 

 those of typical Lcpns, belong to the genus Oryctolagus. The 

 processes are here large, but are not wide and triangular and they 

 do not project out laterally from the sides of the skull as they do 

 in Lepns. The process is arched. The anterior portion does not 

 meet the frontal bone and thus subtends a notch, and a larger pos- 

 terior notch is formed by the posterior angle which also does not 

 meet the cranium. In two skulls of domestic rabbits at hand, a 

 lop-eared and a Belgian hare, the anterior angle or limb of the 

 postorbital process meets the frontal bone, and in the lop-eared forms 

 the outer boundary of an irregular foramen, while in the Belgian 

 hare the whole anterior angle is fused to the cranium, so that even 

 the foramen is obliterated. In both these specimens posterior 

 notches are present. 



3. In the third form of postorbital process, the anterior limb is 

 entirely lacking or else so intimately associated with the cranium 

 that the process appears as a triangle, one whole side of which is 

 attached to the cranium, the second side directed outward and some- 

 what forward, while the third side is directed obliquely inward and 

 backward, forming the outer boundary of a posterior notch. This 

 type of postorbital is found in the genera Roincrolagiis, Pronolagns, 

 Caprolagits, Pcntalagus, and probably in Nesolagiis. The process is 

 larger and blunter in Pcntalagus than it is in the others. 



4. Postorbital processes long and narrow, strongly arched, at- 

 tached to the skull by a very broad and short pedicle. The whole 

 anterior part of the process, with the exception of a millimeter or 

 two, is attached to the skull, so that only a very small notch is sub- 

 tended. The posterior part of the process is long and narrow, not 

 triangular as it is in skulls of the preceding type. Its inner posterior 

 edge touches the side of the cranium, and a narrow clavate slit is 

 thus formed between the inner edge of the process and the side of 

 the skull. In its typical form this slit or clavate foramen is much 

 narrower than the process which helps to make it. In one skull of 

 Syhilagiis tloridanits incanisi. No. 22,409, from Illinois, complete 

 fusion of the postorbital process with the side of the skull takes 

 place, and the clavate foramen is obliterated. The opposite ex- 

 treme is found in the group of Sylz'ilagiis arizoncc and its subspecies, 

 where the clavate foramen is relatively wider and passes gradually 

 over into the next style of postorbital. In these atypical forms the 

 anterior notch is also relatively larger than it is in typical Sylvilagus. 



